What Is Mitral Regurgitation (MR)?

The Mitral Valve between the left atrium and the left ventricle.

The valve has two cusps that meet in the middle like a Bishop’s Mitre Headdress.  When the left ventricle contracts the pressure in the ventricle exceeds that in the atrium and so the valve leaflets close and the blood is expelled out through the aortic valve into the aorta. When the ventricle relaxes, the pressure in the atrium exceeds that in the ventricle and so the blood passes through the valve, opening the two leaflets out of the way, so there is no resistance to blood flow.

The mitral valve is comprised of two thin leaflets.  The integrity of the valve is dependent upon fibrous cords known and the chordae that tether the tips of the leaflets to the left ventricle below, so that the leaflets cannot flip back into the left atrium during ventricular contraction.  this is how the closure of the valve is assured.  However, if the chordae fail to bring the leaflets together, blood will leak or regurgitate through the valve.

The two mechanisms that most commonly cause the failure of the valve and regurgitation are:

Primary valve failure due to Chordae redundancy causing bowing of the valve, or chordae rupture causing part of the valve to flail.

Secondary valve failure due to the enlargement of the left ventricle causing pulling on the otherwise normal chordae and displacing the tips of the leaflets.

When the mitral valve is has stenosed it may be possible to stretch it back open with a balloon (Balloon Mitral Valvuloplasty), or it may need to be surgically replaced.

When the valve is regurgitant, it may be possible to reduce the leak from the leg by a MitraClip procedure or through an open chest operation by surgical mitral valve repair or replacement.

When a valve develops narrowing (stenosis), the speed of blood flow through the reduced opening increases causing turbulence.

When a valve develops leakiness (incompetence or regurgitation), the blood can flow backwards through the valve when it is supposed to be closed causes turbulence.

When there is a hole between chambers of the heart blood will flow from the chamber with higher pressure to the chamber with lower pressure. This can cause turbulence if the flow is fast.

Sometimes there can be an increased flow of blood through a normal heart that can cause turbulence.  This can be found when a patient has a low blood count (anaemia), has an overactive thyroid (hyperthyroidism), fighting a severe infection (sepsis), or even a normal pregnancy.